Power generation machinery, such as steam or gas turbines, are often operated continuously with scheduled inspection and maintenance periods, at which time the turbine is taken off line and shut down. By way of example, a gas turbine engine often will be operated to generate power continuously for approximately 4000 hours, thereupon it is taken off line for routine maintenance, inspection, and repair of any components identified during inspection. Taking a gas turbine off line and eventually shutting it down completely for scheduled maintenance is a multi-day project. Some turbine components, such as the turbine rotor section, are operated at temperatures exceeding 1000° C. (1832° F.). The turbine requires 48-72 hours of cooling time to achieve ambient temperature before complete shutdown in order to reduce likelihood of component warping or other deformation. During the shutdown phase the turbine rotor rotational speed is spooled down from operating speed of approximately 3600 RPM to a speed of approximately 120 RPM or less in “turning gear mode” where the rotor is externally driven by an auxiliary drive motor, in order to reduce likelihood of rotor warping. Other turbine components, such as the turbine housing, are also cooled slowly to ambient temperature.
Once the turbine is cooled to ambient temperature over the course of up to approximately 72 hours internal components of the now static turbine can be inspected with optical camera inspection systems. Known optical camera inspection systems employ rigid or flexible optical bore scopes that are inserted into inspection ports located about the turbine periphery. The bore scope is manually positioned so that its field of view encompasses an area of interest within the turbine, such as one or more vanes or blades, combustor baskets, etc. A camera optically coupled to the bore scope captures images of objects of interest within the field of view for remote visualization and archiving (if desired) by an inspector.
If a series of different images of different areas of interest within a given turbine inspection port are desired, the operator must manually re-position the camera inspection system bore scope to achieve the desired relative alignment of internal area of interest and the field of view. Relative alignment can be achieved by physically moving the bore scope so that its viewing port is positioned proximal a static area of interest. Examples of such relative movement of bore scope and static turbine component are by inserting a bore scope in different orientations within a static combustor or radially in and out of space between a vane and blade row within the turbine section. Relative alignment can also be achieved by maintaining the bore scope viewing port in a static position and moving the turbine internal component of interest into the static viewing field. An example of relative movement of turbine internal component and static bore scope is inspection of different blades within a blade row by manually rotating the turbine rotor sequentially a few degrees and capturing the image of a blade. The rotor is rotated sequentially to align each desired individual blade in the row within the camera-viewing field.
Complete turbine inspection requires multiple manual relative repositioning sequences between the camera inspection system viewing port and areas of interest within the turbine by a human inspector. Inspection quality and productivity is subject to the inspection and manipulation skills of the inspector and inspection team. Inspection apparatus positioning is challenging due to the complex manipulation paths between components in a gas turbine. For example, insertion of a bore scope through a combustor inspection port in order to inspect the leading edge of first row vanes or related supports requires compound manipulations. Improper positioning of inspection apparatus within a turbine potentially can damage turbine internal components. Often an inspection team of multiple operators is needed to perform a manual inspection using known inspection methods and apparatus. In summary, known manual camera inspection procedures and inspection system manipulation are time consuming, repetitive in nature, and often require assistance of an inspection team of multiple personnel. The “human factor” required for known manual camera inspection procedures and inspection system manipulation introduces undesirable inspection process variances based on human skill level differences. Given human skill variances, some inspection teams are capable of completing inspections in less time, achieve better image quality, and have lower inspection damage risk than other teams. Ideally, skills of a high performing inspection team could be captured for use by all teams.
It is also desirable to obtain dimensional information about gas or steam turbines, including gas side internal structures within an industrial gas turbine inspection for extraction of structural information that is useful for off-line engineering studies. For example, it is desirable to obtain structural information about gas side combustor and transition components within the gas side of a gas turbine and generate CAD or other computer images when engineering data files are not available. Previously structural information was obtained by tearing down the turbine after completion of the cool down cycle and thereafter physically inspecting the components with measurement instruments, such as coordinate measurement systems. Physical measurement data were thereafter used to construct CAD or other data files long after engine cool down, thereby adding delay to the maintenance schedule.
It is preferable to gather such structural data prior to turbine tear down so that replacement components can be ordered or fabricated in parallel with the start of maintenance operations rather than wait for visual and/or physical inspection after engine tear down. If dimensional data, preferably with visual data, of turbine internal components can be obtained early and easily in the earliest possible stages of the cool down cycle—for example when the rotor is spinning in the long turning gear mode part of the cool down cycle—components needing repair can be prioritized for replacement, refurbishment and/or other repair days before the turbine rotor comes to a complete rest.
It is also desirable to obtain quantitative information about relative dimensional surface profile of components within power generation machines, such as turbine blade or vane thermal barrier coat (TBC) layer variations, perforations in such surfaces, blade tip gap between turbine blade tips and their opposed abradable surfaces of the turbine engine casing and seal gaps between stationary turbine vane central hubs and their opposing rotating rotor seals. It is preferable to gather such surface profile relative dimensional data prior to turbine tear down, for the previously stated reasons respecting structural data gathering. Surface profile data gathering can be performed separate and apart from other types of visual inspection data gathering.
In many field service applications it is also desirable to gather multiple types of visual inspection data, including dimensional and/or surface profile data and/or a general video record of power generation machine internal components during a single pre-teardown inspection cycle.